Linux+ Unit 04

Course ILT

Exploring Linux filesystems Unit objectives  Discuss the directory structure and file types and use wildcards to specify multiple file names  Display the contents of text files and binary files  Search text files for regular expressions and identify common editors

Course ILT

Topic A  Topic A: Linux files and directories  Topic B: Displaying the contents of files  Topic C: Searching and editing text files

Course ILT

The Linux directory structure

The Linux directory structure Course ILT

 Directory – Special file used to organize other files into a logical structure

 Absolute pathname – Full pathname to a certain file or directory starting from the root directory

Home directory Course ILT

 Home directory – A directory for users to store personal files and information – Each user has a subdirectory

Changing directories Course ILT

 pwd (print working directory) – Used to identify the current directory path

 cd (change directory) – Used to move from one directory to another

The ~ metacharacter and relative paths

Course ILT

~ – Refers to the current user’s home directory – Can specify another user’s home directory by adding the username after ~

 Relative pathname – Pathname of a target directory relative to your current location in the tree

Tab-completion

Course ILT

 Tab-completion – Fills in the remaining characters of a unique filename or directory name when you press the Tab key

Course ILT

Activity A-1

Logging on and navigating the file structure

Course ILT

File types       

Text files Binary data files Executable program files Directory files Linked files Special device files Named pipes and socket files

Filenames Course ILT

 Filename – User-friendly identifier given to a file

 Filename suffixes – Identifiers following a dot (.) at the end of a filename – Used to denote the type of the file

Course ILT

Filename extensions, continued

Course ILT

The ls command  Used to list the files in a directory  Most common method for displaying files  Displays all the files in the current directory – You can use an argument with ls to list a directory different from current one

Course ILT

Ls –F file type characters     

@ Linked file * Executable file / Subdirectory = Socket file | Named pipe

The file command Course ILT

 File command – Displays detailed information about any file – Works with multiple files – Uses * to include all files in a directory

Hidden files Course ILT

 Hidden files – Files that are not normally displayed with common filesystem commands – Represent important configuration files or program directories

Course ILT

ls command options

continued

Course ILT

ls command options, continued

Course ILT

Activity A-2

Examining files and file types

Course ILT

Wildcard metacharacters  Can simplify more than one filename to a command  Interpreted by the shell and can be used with most filesystem commands  Matches certain portions of filenames or an entire filename

continued

Course ILT

Wildcard metacharacters, continued

Course ILT

Activity A-3

Using wildcard metacharacters

Course ILT

Topic B  Topic A: Linux files and directories  Topic B: Displaying the contents of files  Topic C: Searching and editing text files

Displaying content of text files Course ILT

 cat command – Display the entire contents of a text file to the screen

 tac command – Displays a file to the screen beginning with the last line of the file and ending with the first line of the file

 head command – Displays the first 10 lines (including blank lines) of a text file to the terminal screen – Can also take a numeric option specifying a different number of lines to display continued

Displaying content of text files, continued

Course ILT

 tail command – By default, displays the last 10 lines (including blank lines) of a text file to the terminal screen – Can also take a numeric option specifying a different number of lines to display

Other text file viewing commands Course ILT

 more command – Displays a text file page-by-page and line-by-line on the terminal screen – Gets its name from the pg command once used on UNIX systems

 less command – Displays a text file page-by-page on the terminal screen – Use the arrow keys to navigate the file

Course ILT

Activity B-1

Displaying text file contents

Displaying the contents of binary files

Course ILT

 strings commands – Linux command used to search for and display text characters in a binary file

 od command – Linux command that is used to display the contents of a file in octal format (numeric base 8 format) – Safe to use on binary files and text files

Course ILT

Activity B-2

Displaying binary data

Course ILT

Topic C  Topic A: Linux files and directories  Topic B: Displaying the contents of files  Topic C: Searching and editing text files

Searching for text within files Course ILT

 Regular expressions (regexp) – Special metacharacters used to match patterns of text within text files – Commonly used by many text tool commands such as grep

Course ILT

Using regular expressions        

grep awk sed vi emacs ex ed PERL

Course ILT

Regular expressions and wildcards  Wildcard metacharacters are interpreted by the shell; regular expressions are interpreted by a text tool program  Regular expressions match characters within text files; wildcard metacharacters match characters in filenames or directory names

continued

Course ILT

Regular expressions and wildcards, continued

 Wildcard metacharacters regular expressions usually have different definitions than wildcard metacharacters  More metacharacters are available for regular expressions  Regular expressions are divided into two different categories: – Common – Extended

Course ILT

Regular expressions

The grep command Course ILT

 grep – Displays lines in a text file that match a common regular expression

 egrep – Displays text that matches extended regular expressions

 fgrep – Does not interpret regular expressions – Returns results faster than the egrep command

Course ILT

Activity C-1

Using regular expressions in grep and egrep

Course ILT

The vi editor  One of the oldest and most popular text editors available for Linux and UNIX operating systems – vim is an improved version for Linux – Not easy, but portable

continued

Course ILT

The vi editor, continued  The vi editor is called bi-modal because it functions in two modes: – Command mode  Performs editing tasks not related to inserting text

– Insert mode  Allows inserting text into the document

Course ILT

Entering insert mode using keyboard keys

Course ILT

Key combinations

continued

Course ILT

Key combinations, continued

continued

Course ILT

Key combinations, continued

Course ILT

Key combinations used at : prompt

Course ILT

Activity C-2

Using the vi editor

Course ILT

Activity C-3

Exploring vi options

Course ILT

Other common text editors  pico (PIne COmposer) editor  mcedit editor (Midnight Commander Editor)  emacs (Editor MAcroS) editor  xemacs editor

Course ILT

emacs editor  Alternative to the vi editor that offers equal functionality  Not an easy-to-use editor as it must memorize several key combinations to work effectively

continued

Course ILT

emacs editor, continued

Course ILT

xemacs editor  Version if emacs that runs in the KDE or GNOME GUI environments  Much easier to use than emacs  May not be available in every Linux distribution that contains a GUI environment

Course ILT

xemacs editor, continued

Graphical text editors Course ILT

 nedit editor

gedit editor Course ILT

 gedit editor – Text editor for the GNOME desktop

Kedit editors Course ILT

 Kedit editor – Text editor for the KDE desktop

Course ILT

Activity C-4

Discussing common text editors

Course ILT

Unit summary  Learned about the Linux directory structure and Linux files, and used shell wildcards to specify multiple file names  Displayed the contents of text files and binary files  Searched text files for regular expressions by using grep, and identified common editors  Used the vi editor